Having excellent mechanical characteristics, fiber reinforced composite materials comprising, as the intermediate bases, prepregs that comprise reinforcing fibers and matrix resin are now widely used in sporting good, such as fishing rods, arrows, golf shafts and the like. Such composites are also used in the aerospace industry and other general industries since they are light in weight and excellent in mechanical properties.
Various methods are employed to produce fiber-reinforced composite materials. Above all, a method of using a prepreg, which is a sheet-like intermediate base to be prepared by impregnating reinforcing fibers with a matrix resin, is popularly used. Using this method, shaped articles are made by laminating a plurality of such prepregs followed by heating the resulting laminate.
Demand for lighter weight products in sporting goods with high strengths are desired. In particular, bending strength of thin tube structures like fishing rod tips, the durability and survival in the field from extreme use, is most desired. By improving the strength and durability of the fiber reinforced materials, lighter weight products can be produced at the same strength as current materials. This allows for either higher strength products at current weights or lighter weigh products at same strength. Both of which have benefits to the manufacture and consumer.
In recent years, sporting goods are being reduced in weight to maintain a marketing dominance (edge). This demand for lightweight designs requires stronger lighter weight materials. The breakage rate of these designs must maintain equal to or be improve over current products. The consumer will not accept lighter weaker sporting goods, nor will the manufactures. Of course, designs in the shape and lay-up can and has reduced the weight. However, this is now at the limit and improvements in resin/fiber system are necessary to push that limit.
In most cases lighter weigh also equates to better performance. Finished products in which weight has been removed require less energy to move are more efficient and usually more appealing to the consumer. The industry is requesting prepreg manufactures to invent stronger materials or improve existing materials to produce lighter weight products.
Matrix resins used for prepregs include both thermosetting and thermoplastic resins, but in most cases thermosetting resins are used. Epoxy resins are mainly used since they are easier to handle and process, have excellent mechanical and chemical properties such as heat resistance, stiffness, dimensional stability and chemical resistance.
Known methods to improve epoxy resin modulus and toughness include Japanese patent Publication No. 58-005925 which disclosed has high modulus, but paid no attention to improving tack and toughness. Another example is Mitsubishi Chemical (U.S. Pat. No. 5,302,666) which has adequate tack and toughness by utilizing bisphenol A type epoxy and solid rubber, however these techniques sacrifice modulus because of the formulation of the epoxy resin. Another example is Cytec patent U.S. Pat. No. 6,013,730 however this patent uses a solid rubber. To utilize solid rubber, it should be dissolved in solvent prior to use and remaining solvent in resin formulation causes voids in cured composite, which would weaken mechanical strength. Furthermore, this patent formulation may produce a resin that is too high in viscosity for making tubular products. Other examples of high modulus toughened systems are: Matsushita Japanese Patent Laid-Open No. 2001-302887 which discloses the combination of phenol novolak epoxy and a particle rubber to achieve high modulus and toughness, however such formulation gives insufficient tack. Toho Tenax U.S. Pat. No. 4,500,660 disclosed the combination of phenol novolak epoxy and tetrafunctional (TGDDM) resins, solid rubber and liquid rubber to obtain high adhesion between honeycomb core and Prepreg, however such formulation does not show high enough modulus.